Cable and pay-per-view television programming are extremely popular and widely available in modern society. Those firms providing such programming are frequently lucrative and successful. This success comes from the ability to prevent those who have not purchased the service from receiving and using the audio-visual signals transmitted by the service provider.
In general, it is common for a cable company or other service provider to scramble its signals to prevent their use by unauthorized parties. This scrambling is intended to make the signals unintelligible to typical television sets which are not authorized to receive and use the scrambled signal. When the signal is scrambled, a conventional television will not recognize the signal, or at best, display a distorted image from the signal.
Cable companies which provide a number of channels over a cable connection may only scramble certain channels so that cable subscribers can be required to pay additional fees for receiving these "premium" channels. The premium channels are typically movie or adult channels.
Those subscribers who have paid the service provider for reception of the scrambled signal will be given equipment for use with their television sets which unscrambles the signal. With this equipment, the authorized user can unscramble and receive the service provider's signals and view the programming contained in the transmission.
A well-known conventional method of scrambling a signal to prevent its unauthorized reception is to reverse the spectral positions of the audio and video portions of the signal. Typically, an audio-visual signal will have an audio carrier signal at a first frequency and a video carrier signal at a second frequency. The carrier signals are modulated to carry the respective video and audio data of the transmitted programming.
If, however, the audio carrier signal is transmitted at the second (video carrier) frequency, and the video carrier signal is transmitted at the first (audio carrier) frequency, the signal is scrambled. A television tuner will be attempting to receive the audio signal at the first frequency and the video signal at the second frequency, and will be unable to receive the reversed signal properly.
Many other methods of scrambling audio-visual signals during transmission are known in the art. However, all are subject to various deficiencies. For example, many scrambling methods are only partially effective. Thus, while the scrambled signal is not received clearly, the image and audio may still be intelligible.
Accordingly, there is a need in the art for an improved and more effective means and method of scrambling an audio-visual signal.